Method for eliminating hollow defect in atomized alloy powder

Abstract

The invention relates to a method for eliminating hollow defects in atomized superalloy powder, and pertains to the field of powder metallurgy materials. A ball-milling processing is conducted on the atomized alloy powder to eliminate the hollow defect, obtain solid powder and increase powder utilization efficiency. By controlling mill ball diameters, mass ratio of mill balls with different diameters, mass ratio of ball to powder and ball milling time, a multi-directional impact on the powder is achieved, thereby control powder shape and obtain solid spherical powder. The invention eliminates powder hollow defect by using ball milling process and equipment. This invention with high powder utilization efficiency, short ball milling time and simple operating process, can be used for large-scale preparation and application.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a method for eliminating hollow defects in atomized superalloy powder, and pertains to the field of powder metallurgy materials.BACKGROUND OF THE INVENTION[0002]The gas atomization of melting alloy is a main method for superalloy powder preparation. However, a main problem raised in such a method is that a large amount of prepared powder may contain closed pores filled with atomizing gas, which is defined as hollow powder. The hollow defects in power is completely sealed, which is difficult to be eliminated in subsequent powder-forming process. Thus, the hollow defects will remain in the materials and finally form pores. In the meanwhile, residual gas sealed in hollow defects will expand during subsequent heat-treatment and service. All of those factors lead to the formation of heat-induced pore, or heat-induced crack, which severely deteriorates materials mechanical properties, especially for powder metallurgy superalloy....

AI Technical Summary

Benefits of technology

The present invention is about a method of making solid powder from atomized alloy powder by controlling the condition of ball milling, such as the ratio of mill balls and the mass ratio of ball to powder. This method can remove unqualified hollow powder and improve the solidification microstructure of the powder. It can also be used for large-scale preparation and application with high powder utilization efficiency.

Problems solved by technology

However, a main problem raised in such a method is that a large amount of prepared powder may contain closed pores filled with atomizing gas, which is defined as hollow powder.

The hollow defects in power is completely sealed, which is difficult to be eliminated in subsequent powder-forming process.

Thus, the hollow defects will remain in the materials and finally form pores.

All of those factors lead to the formation of heat-induced pore, or heat-induced crack, which severely deteriorates materials mechanical properties, especially for powder metallurgy superalloy.

Therefore, hollow powder is one of the main sources of those defects, and severely deteriorates superalloy mechanical properties.

In countries such as America and Russia, atomized powder of which particle size is less than or equal to 53 μm (−270 meshes) or 45 μm (−325 meshes) is generally used to prepare superalloy to reduce adverse impact of the powder hollow defect on alloy mechanical properties, but it will cause lower powder utilization efficiency and higher cost.

By using the sieving method, large-size hollow powder can be removed, but hollow powder can also generated from undersize particles, which makes the eliminating process incomplete.

Moreover, sieving method to remove hollow powder usually suffers low powder utilization efficiency, serious waste and increased cost of alloy preparation.

When the atomized gas pressure is reduced, the quantity of hollow powder is also reduced, but the content ratio of large-size powder is high, and the yield of fines is low.

Consequently, the microstructure of solidified powder becomes bulky.

For superalloy powder fabricated by argon atomization (AA), detailed process for eliminating powder hollow defects has not been reported, and features of gas atomization technique cause that controlling parameters during the atomization process can only reduce hollow powder ratio, not completely eliminate the powder hollow defect.

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